[UPDATE April 1 via BigBoss): To All: “Saurik just released mobilesubstrate 0.9.2805-1. This version fixes the problem entirely allowing for mobilesubstrate addons to work with Skype app. You can now use Skype app with VoIPover3G!"

[UPDATE, Read carefully]
“To fix the Skype crash, all mobilesubstrate based hacks are disabled on the Skype app. This means you cannot use voipover3g or backgrounder with Skype app. Do not ask how to do it or point out that it doesnt work. The developer of mobile substrate has already stated that it will not work."more info